Electron device



Imca-aon mzvrcs fund Jun 16. 195e 2 Sheets-Sheet 1 INVENTOR. -UR T D/EL` BY ATTORNEY.

April 16, I1940. K. DIELS ELEGTRON DEVICE Filed June 16, 1938 2 Sheets-Sheet 2 H 5 7 I v -IM {Q1/W -fl/m V/ :Lf -LY ,J j "x 6 f ATTORNEY.

Patented Apr. 16, 1940 ELECTRON DEVICE Kurt Diels, Berlin-Friedenau, Germany, assignor to Telefunken Gesellschaft fr Drahtlose Telegraphie m. b. H., Berlin, Germany, a corporation of Germany Application June 16,

1938, Serial No. 213,955

In Germany June 10, 1937 4 Claims.

This invention is concerned with a novel type of electron source for cathode ray tubes, especially those used for television work. The chief desideratum in the operation of such tube.. is to produce an intense and sharply focused spot upon the imaging surface, that is, a spot which will always preserve its focused and concentrated condition unaltered, even upon modulation of the intensity of the beam of electrons. 'I'he sharpness or the focus of the spot essentially is predicated upon three factors, to wit:

(l) Sharp geometric definition of the electronic sourse, this meaning both real and 'virtual sources of electrons;

(2) A constant eld intensity of the elds presenting axial symmetry and employed forrimaging the electron source; and

(3) Homogeneousness of the cathode rays emerging fromthe real or the. virtual electron source, and an unvaried angular distribution of the same even upon modulation of the number of electrons in the beam.

Attempts have been made in the prior art to meet the rst named condition. However, the second and the third conditions where modulation of the cathode ray is used, has not been fulfilled because of the difilculties that modulation of, that is control of the intensity of the beam, is associated with alterations of the field intensity of the particular electron optical system to be imaged or focused, or an alteration of the velocity and/or the angular distribution of the electrons. Any suggestions that have heretofore been suggested with a view to obviating these drawbacks involve comparatively complicated technical means and expense and have not been satisfactory. The present invention discloses a simpler solution of the problem, and it indicates a way to create a so-called punctiform or highly concentrated source of electron supply which surpasses all similar sources of electrons disclosed in the earlier art as regards working life, yield, and homogeneity of emission, especially where the beam is modulated in intensity.

The basic idea of the invention shall be described more fully by reference to a cathode ray tube for television receiver purposes. The basic idea is that the pencil or jet of cathode rays issued from a powerful thermally emitting cathode is caused to bombard, after modulation, a secondary emission impactor surface of reduced dimensions having the shape of the object to be imaged. This impact or target surface, in contradlstlnction to the thermally emissive cathode,

acts and serves as the cathode properly so-called of the main path of the pencil of rays, and the same, directly or indirectly, is imaged upon the luminescent fluorescent screen'or the like. The total emission of the `heated cathode forming an U element of the cathode arrangement may be far higher than the emission of a heated cathode of the sort heretofore used in cathode ray tubes since it is not material and essential whether the same is punctiform or not.

A further increase in the yield of electrons may be secured by secondary electron multiplication on the target surface struck by the primary electrons. Modulation is effected in thepath of the rays of primary electrons, in such a way that the fields of the main beam having axial symmetry stay practically undisturbed. In this connection, care must be suitably taken so that the primary electrons will flow through only a tiny aperture into the field of an electrode` pertaining to the main pencil path with the result that the field thereof remains practically undistorted. Modulation is insured either by virtue of velocity variation and/or by variation of the volume of primary electrons impinging upon the .5 target-surface. Variation of the volume or quantity could be accomplished by grid control or else by disposing the target surface as the base of a cone whose angle will vary in unison with the modulation. Moreover, the pencil or beam of .0 electrons can be deflected unilaterally before impinging upon the target, or else upon a diaphragm or stop mounted at a point intermediate between the heated cathode and the target surface. No matter which of these different modes of modulation be used, the result is that the velocity and the angular distribution of the electrons issuing from the target surface stay substantially constant independently of the modulation. This fact is extremely important for a clean cut electron optical image of the target surface in the main ray pencil, under conditions independent of the modulation.

For further explanation of the disclosure, reference shall be made to the appended drawings where Fig. 1 shows diagrammatically one embodiment of the invention, while Fig. 2 shows a modification of the embodiment shown in Fig. 1.

The pencil of electrons issuing from the heated cathode l is subjected to the action of control modulation electrode 2, and it then enters into the opening 3 of the cylindrical electrode 4. In conjunction with the coaxially disposed electrode 5 maintained at a different potential, the said electrode 4 furnishes an electron lens field which I will collect or condense the electrons in such a way that they will essentially impinge upon the target 6. A small aperture of the electrode 6 terminatesand issues into the cylindrical elec trode 1 of they main ray path being kept at the same potential. The target surface 8 has the form of a planar circular diskghowev'er, this disc may have an inwardly or outwardly directed curvature or it may be made annularly in shape.

In order to secure anemission which will present a geometrically sharp contour or line of demarcation, it is advantageous to de-activate the parts surrounding the target surface, insofar as primary electrons will bombard them, so as to preclude the chances of secondary electrons bei ing given off thereby. VThat is to say, the said parts could, for instance, be .roughened or granulated, or it may be convenient to coat the same with substances such as zirconium, zirconia, or carbonaceous material. The target itself it preferably kept at a definite potential, and the target material used may be nickel, which possesses said aperture thereupon being imaged and focused upon the fiuorescent screen i0 'by the aid of the lens field created between the electrodes 8 and i4.

If desired. as shown in Fig. 2, another reduction stage could be inserted, which would consist of the lens field set up betwen the electrodes 8, Il, and i2.

Having described my invention, what I claim 1. A cathode ray tube comprising an envelope having an electron receiving screen mounted within the envelope, a secondary emissive surface displaced from and parallel to the screen, an electron optical system positioned intermediate the screen and secondary emissive surface, means for projecting a beam of electrons from a thermionic cathode upon the secondary emissive surface to eject secondary electrons therefrom said secondary emissive surface having an area smaller than that of the said cathode, and a unitary electrode common to both said electron optical system and said beam projecting v means.

2. A cathode ray tube comprising an envelope having a luminescent screen mounted within the envelope, a secondary vemissive surface displaced from parallel to the luminescent screen, an electron optical system positioned intermediate the screen and secondary emissive surface, andv means including a source of electrons to develop a beam of electrons, said source of electrons having an area larger than the area' of the secondary emissive surface, means to project the developed-beam of electrons upon the secondary emissive surface, means to control the intensity of the developed beam of electrons in accordance with signalling potentials, and a unitary electrode common to both said electron optical system and said beam projecting means.

3. A cathode ray tube comprising an envelope having a luminescent screen mounted within the envelope, a secondary emissive surface displaced from and parallel to the luminescent screen, an electron optical system positioned intermediate the screen and secondary emissive surface, means including a source of electrons to develop a' beam of electrons, said source of'electrons having an area larger than the area of the secondary f for projecting a beam of electrons upon the secondary emissive surface, said electron emitting surface having anarea larger than said secondary emissive surface, means to control the intensity of the beam of electrons in accordance with signal potentials, and a unitary-electrode common to both said electron optical system and: n

said beam projecting means.

, KURT DIELS. 

